Orney



P H. P. VASSAR THERMORESPQNSIVE MEASURING INSTRUMENT- Filed Aug. 6, I942 INVENTOR %:a%

' -%TTORNEY WITNESSES:

. see is. 1945 e 2383M l lTED STATES PATENT OFFICE 2,385,044 THEBMORESPONSIVE MEASURING INSTRUMENT Hervey P. Vassar-{Bloomfield N. ,L, asslznor to Westinghouse Electric Corporation, East Pitts-'- burzh, Pat, a corporation of Pennsylvania Application sumo, 1942, Serial No. use i I 1 claims. ci. 111-05) invention relates to thermore's'nonsive dea current proportional to the variable quantity vi, and it has particular relation to "a themeto be measured through both of the multimetallic Wt; device for measuring currents flowing elements-in series. eiectriccl circuits. Since the multimetsliic elements are dinertorcue, d low maintenance, thermoresponsivo tallic n s w r 1, th P c le of emdevices, such es demand wattmeters, have been rent throush both elements in series would have favorably received {or measuring variable quan- Substantially o effect on the P i of the titles. A device for this purpose generally come c To P i e mov ment of the shaft which prises e pair or thermoresponsive elements, such is dependent n the V ria l q ti y t e cc flexible fluid containing elements or multimemeasur wi i e lll o lements are detnllic elements, diilerentially associated with-an slined to respond differently to current passnnccuse of. their sturdy construction, mini entislly associated wi h a h r t the l I m; b Devices of t type are m in: therethrouzh. To this end, the multime- 1 acted i Un t st t t t 1,15 ,412, 1,417,. talllc elements may havesubstantlally diflerent out and 2,13%29. Theexpression multimee t i l mistuwes- Since eat-generated by wherein st least. one lamination has a. temperav r in coral-n06 with the 1' tin'e coecient of expansion which differs from lows that the heat. to which each muitimetalllc It of mother one or the lsminations. v element is subjected is depen t on the r iioimeasuring l tr m them once thereoi. For thisreason. the same current device m have a pair of th'ermoresponsive ele- "P throush both of the multimetallic elemcnte ectm diflerentlglly on m Because ments in series produces a resultant differential defines a laminated metallic structure current P 8 W011!!! i l tric l resistance oi the einerentiai reationship of the thermoretorque mu on the-shaft which pendent eve elements, ambient temperature variamime quantity to be meuumditem do not eflect the accuracy of the measuring Preferably the multimetsllic elements re'dedevice. is the temperatures of the thermo filmed with the s e deflection and torque onresponsive elements diner, a difl'erential torque is stants relative to temperature variation. with applied in the him; which correspond, to the gsuch a construction. the shalt is substantially reel iii temperatures of the elements. Such Inflected b! emblem temperame 5 emncg in bemmrature ma be b therefore, an 0.! il-Wention pine an electrical resistance heater adjacent pmvide an lmmv mermmmve new? one of the thermoresponsive elements and en- It 15 5 01 thil'mvenflim t N er the heater in accordance W th a variable themmmamm" device" memo ea! c) w 4. in i: .11 is l t t mumg 5mm p shaft with means to: passing electrical current out No. 2,212,730. 4

it provision of a separate heater isundeslrm i masons that m nn w M an It is another obiect-ot the invention to provide I'r'roi and indirect heating is somewhat less thermommmlve v to be magma A device or responsive-elements diilerentiallv connected to a 5 directly through both a: the thermoresponslve mei t. direct heating, At the me time, 0 metallic elements diilerin: in electrical. resistto the thermoresponsive elements which would increase the load on the shaft asso- It is 01 the invenflim t0 cictcc eiewith should be avoided, vi a h l u rinz instrumenthsvme i. i. with the invention a opposed multimetallic elements having diiierent @mmmve 616mmmcludm m to electrical resistances connected in a series cir-. element and a compensating element W elmt'bdnm Broth energized. in accordance with a variable t commits to be measured. In a specific emb'oai "immmtwmmtmthe following description taken in conjuncg tion with thc accompanying drawing, in which: rnentoic electrically and mechanically connected me 1 is an exploded view in perspective to cm oi the other multimetallic element. An with parts shown schematic lly o a t ermo eeicgctsicgag circuit then is connected to the tree iv l l yinz the invention: and can t of invention, a Pair of muitimetallic' other Obie! of the invention vfllbe w 'multimetallic elements i'or passing J5 2 is a view in tront elevation of the thatmember in any suitable manner.

moresponsive device illustrated in Fig. 1 with parts added.

Referring to the drawing, Fig. 1 shows a thermo-responsive device having an actuating assembly I which includes two thermoresponsive elements 3 and 5. In the specific embodiment illustrated in Fig. 1, the thermoresponsive elements take the form of spiral multimetallic springs having their inner ends attached, respectively, to collars l and 9 which are secured to a shaft H. At one end the shaft it is provided with a pointer i3 or ther suitable device for actuation in accordance with the rotation of the shaft.

For supporting the actuating assembly i, a housing is provided which includes a base member and cover-members I1 and I9. This housing may be formed of material having suitable heat and electrical insulating properties, such as phenolic resin.

In order to minimize the transmission of heat between the multimetallic elements 3 and 5, the base member I5 may be divided into two portions 2| and 23 which are separated by an air space and which are connected by webs 25 having small cross sections and positioned below a major portion of the space occupied by the multimetallic elements 3 and 5.

The portions 2| and 23 of the base member are provided, respectively, with chambers El and 29 for receiving the elements 3 and 5. In addition, the base member l5 carries abutments 3i and 33 having threaded openings 35 and 36a therein. When the elements 3 and 'e' are in mounted position in their chambers 2i and 25, their outer ends may be attached to the abutments 3| and 33 in any suitable manner, as by machine screws 35 which pass through openings in the ends of the multimetallic elements for threaded reception in the threaded openings i and 36a.

To permit rotation of the shaft ii relative to the housing, the shaft is provided with a pair of bearings 31 and 39 having flanges 37a and 39d. For the reception of these bearings, the base member [5 is provided with recesses having semicylindrical surfaces 5! and Q3. Each of these surfaces has associated therewith a concentric groove Ma or 43a for receiving, respectively, the flanges 31a and 39a of the bearings. Additional passageways Ml for the shaft it may be provided as required.

In order to complete the enclosure of the actuating assembly, each of the cover members is provided with chambers, semi-cylindrical surfaces, and grooves which correspond to the chambers 21 and 29, the surfaces 4i and 38, and the grooves lla and 330. of the base member iii. The cover members may be secured to the base As illustrated, the base member is provided with four abutments 35 each having a threaded opening 55c. Each of the cover members is provided with a pair of projections il having openings lla, which are aligned with a pair of the threaded openings 65c when the cover members are in mounted position on the base member. Suitable machine screws 49 then may be passed through the openings 41a into the threaded openings 15a. for securing the cover members to the base member.

The multimetallic elements 3 and 5 are designed to act differentially on the shaft i 5. Such action may be obtained by mounting the elements with their convolutions wound in opposite directions, as clearly illustrated in Fig. l.

aaeaoas For the purpose of discussion, it will be assumed that when the temperature to which the elements are subjected is raised, the element 3 urges the shaft l: in the direction of the arrow to, whereas the element 5 urges the shaft ii in the direction of the arrow 5a.

In order to energize the elements 3 and 5, the inner end of the elements are connected not only mechanically but electrically. This connection may be effected by forming the shaft ii of an electroconduc'tive material, such as brass or steel. An electrical current dependent on the variable quantity to be measured then is passed through the elements 3 and 5 in series. This current may be either a direct current or an alternating current. For the purpose of discussion, it is assumed that the current is an alternating current which alternates at a conventional frequency of 60 cycles per second. The elements may be energized from a single phase, two or three-wire system, or a polyphase system in accordance with current flowing therein. In the specific embodiment of Fig. l, the secondary winding of a current transformer 51 is connected in any suitable manner to the outer ends of the elements 3 and 5. The .primary winding of the current transformer 5| is included in one conductor of a circuit 53 which supplies current from an incoming line to a load. Consequently, the elements 3 and 5 are energized in accordance with load current flowing in the circuit 53.

If the elements 3 and 5 were exactly similar, current flowing therethrough would produce no displacement of the shaft ii. This is true despite the fact that current flowing through the resistance of the elements would produce heat and would raise the temperatures thereof. The increase in torque applied to the shaft by one element would be compensated by that of the other element.

in order to produce a rotation of the shaft which is dependent on the magnitude oi the ourrent flowing through the multimetallic elements, the elements are designed to respond differently to the current flowing therethrough. onveniently this may be effected by constructing the elements 3 and with different electrical resistances. For the purpose of discussion, it will be assumed that the element 5 has a substantially higher resistance than the resistance of the element 3.

Becaus of the difference in resistances of the elements, the same current flowing therethrough produces more heat in the element 5 than in the element 3. For this reason, the temperature of the element 5 is raised to a higher value than that of the element 5. Since the deflection and torque developed by a multimetallic element is dependent upon the temperature to which it is raised, it follows that the elements 3 and 5 may be designed to deflect the shaft H in accordance with the electrical current flowing therethrough.

As previously pointed out, it is desirable that both of the elements 3 and 5 have similar torque and deflection constants with respect to tem-. perature With such a construction, an equal variation in temperature of both of the elements has no effect on the position of the shaft ii. Consequently variations in ambient temperature would not affect the position of the pointer 83.

As examples of suitable materials for the multimetallic elements, the high resistance bimetallic element 5 may be formed from a layer of material having a low temperature coefficient of expansion, such as a 36% nickel-iron alloy, and a layer of material having a high temperature coefficient f expansion, such as an iron alloy containing approximately 15% nickel, 10% manganese,

and aluminum.

Th low resistance element 3 may be formed from a layer of material having a low temperature coefficient of expansion, such as a 36% nickel-iron alloy, an intermediate layer of high conductivity copper-cadmium alloy, and a layer of material having a high temperature coefficient of expansion, such as an austenitic nickel-chromium steel.

Multimetallic materials of the foregoing types are marketed by the H. A. Wilson Companyof Newark, New Jersey, under the trade designations R440 and R39. The high resistance material has a resistivity slightly greater than eleven times the resistivity of the low resistance material. Despite this substantial difference in resistivities", the two multimetallic materials have substantially the same torque and deflection constants with respect to temperature. When these materials are employed, the elements 3 and 5 may be formed with equal dimensions.

To permit adjustment of the thermoresponsive device, a spring 55 has one end connected to an arm 51 which is attached to a collar rotatably mounted on the shaft II. This collar is secured in any desired position by means of a setscrew 59. The remainingend of the spring 55 is connected to a screw 6| which passes through an opening in a post 63 and has an adjustin nut 65 on its outer end. The post 63 is designed for insertion in a pillar 61 formed on the base member i5.

To adjust the thermal device, the setscrew 59 is loosened and the pointer i 3 is turned to its zero position. With the pointer in this position, the setscrew is tightened. This adjustment renders the zero position of the pointer l3 independent of the tension of the spring 55. The thermoresponsive device then is energized by a predetermined current for a time suillcient to carry the pointer I 3 to predetermined position on a scale 69 associated with the pointer l3. If the pointer l3 fails to move to the required position, the nut 65 is operated to vary the tension of the spring 55 sufficiently to bring the pointer l3 to the required position. This adjustment is disclosed in greater detail in the aforesaid Patent 1,417,695 and in my copending application, Serial No. 394,260, filed May 20, 1941, which has issued as Patent 2,323,738.

Although the information conveyed by the pointer l3 alone may suffice, it sometimes is desirable to provide a frictionally held pointer H for indicating the maximum advance of the pointer 13 over a predetermined period. For this purpose, the pointer [3 may be provided with a lug it which engages the pointer H and advances the pointer II when the pointer I3 is actuated beyond the position initially occupied by the pointer 11. The frictionally held pointer II maintains a maximum position to which it is advanced. Such pointers are well known in the art, and are illustrated in the aforesaid Patent 1,417,695,.and in my aforesaid copending application.

It is believed that the operation of the thermoresponsive device thus far described is apparent from the foregoing description.- If it is desired to measure current flowing inthe circuit 53, the fixed ends of the elements} and 5 are connected for energization' -in' accordance with the current to be measured. .InFig. 1, such energization is efiected through the current transformer 5|. This connection results in the flow f current through the elements 3 and 5 in series. Since the element 5 has a resistance substantially higher than that of the element 3, the heat to which it is subjected and the temperature to which it is raised are substantially higher than the corresponding heat and temperature of the element 3. and 5 have similar deflection and torque constants, the higher torque developed by the element 5 operates to rotate the shaft ll until the actuating torque of the element 5 and the compensating torque of the element 3 are again substantially equal.

The time required for the pointer l3 to reach a new position following a change in the current flowing through the bimetallic elements 3 and 5 depends upon the thermal lagging of the complete thermoresponsive device. In certain cases, a lagging is desired which will bring the pointer l3 to of the total movement required by the change in energization in a period of 15 minutes. Such lagging is well understood in the ar Should the ambient temperature to which the thermoresponsive device is subjected change, the temperatures of the elements 3 or 5 increase or decrease by the same amount. Since the elements 3 and 5 are differentially related with respect to' the shaft H, and since they have substantially equal deflection and torque constants with respect to temperature, such variations in ambient temperature have substantially no effect on the position of the shaft l I and the pointer II.

It should be observed that a thermoresponsive device designed in accordance with the invention requires no separate heating elements. The actuating element 5 and the compensating element 3 serve as heaters. This arrangement provides optimum thermal efficiency.

Despite the supply of current directly to the multimetallic elements no auxiliary flexible connections thereto are required. Consequently the friction loads introduced by flexible connections are avoided.

Although the invention has been described with reference to certain specific embodiments thereof, numerous modifications are possible. Therefore, the invention is to be restricted only by the appended claims as interpreted in view of the prior art. 1

I claim as my invention:

1. In a measuring device for measuring a function of an electrical current over a substantial range of variation thereof, first thermoresponsive means having a first response to a. variable quan tity, second thermoresponsive means having a response to said variable quantity which differs from said first response, each of said thermoresponsive means comprisin a pair of metallic elements having different temperature coeflicients of expansion, means for energizing said first and second thermoresponsive means in accordance with said variable quantity, and means differentially controlled by the responses of said first thermoresponsive means and said second-thermoresponsive means, said first thermoresponsive means and said second thermoresponsive means having similar responses to ambient temperature variations, whereby said differentially controlled means is substantially independent of ambient temperature variations.

2. In a thermal device for measuring a function of an electrical current over a substantial range Since the elements 3 

